Carbon nitride, C.sub.3 N.sub.4, can exist in two possible phases designated .alpha.-C.sub.3 N.sub.4 and .beta.-C.sub.3 N.sub.4. It has long been predicted that crystals of .beta.-C.sub.3 N.sub.4, if they could be made, would possess exotic characteristics such as a hardness exceeding that of diamond, a high energy bandgap and transparency to UV light. Unfortunately, efforts to synthesize this material have produced only amorphous material or impure carbon-rich phases. A continuous coating of crystalline .beta.-C.sub.3 N.sub.4 has not heretofore been obtained, and films exhibiting the predicted properties have not been realized.